This application claims the priority of German patent application 196 42 832.7, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for controlling a compressor of a motor vehicle air conditioner designed for variable power draw and driveable by the vehicle drive.
A method of this kind is described in German patent document DE 38 43 924 C2. In the air conditioner disclosed in this document, the thermal load on the system is detected and the required compressor intake pressure and the drive torque required to provide it are determined for the compressor. During those time intervals in which the engine provided as a vehicle drive is running at idle, the idle rpm is increased to enable the determined compressor drive torque to be delivered without the engine stalling. If the engine is already running at an increased rpm, the drive torque for the compressor is drawn from the engine drive torque that serves to drive the vehicle.
Furthermore, in motor vehicle air conditioners with compressors driveable by the vehicle drive, it is already known to switch off the compressor temporarily during those vehicle operating phases in which the driver calls for powerful vehicle acceleration, for passing maneuvers for example, in order to have available all of the driving torque generated by the vehicle drive for driving the vehicle. This measure is described for example in European patent document EP 0 288 658 B1.
There is a need for that allows an air conditioner to operate even during powerful acceleration maneuvers without significantly adversely affecting the ability of the vehicle to accelerate.
This and other needs have been met according to the present invention by providing a method for controlling a compressor of a motor vehicle air conditioner, the compressor being designed for variable power draw and driven by the vehicle drive, characterized in that the power draw of compressor is subject to an upper limit that is set as a function of the difference between the maximum drive torque that the vehicle drive can deliver to the drive torque required for driving the vehicle.
This and other needs have also been met according to the present invention by providing a method for controlling a variable-power air conditioner compressor in a motor vehicle, comprising the steps of: determining an engine torque value required to drive the air conditioner compressor to achieve a cooling level requested by a user (T.sub.ACreq) ; determining a maximum available engine torque value (T.sub.max); determining an engine torque value required for vehicle movement; and setting an actual torque fed to the variable-power air conditioner compressor (T.sub.act) to the lesser of: (i) T.sub.ACreq ; and (ii) T.sub.max -T.sub.drive.
According to the present invention, the power draw of the compressor is subject to an upper limit that is set variably as a function of the difference between the maximum drive torque that the vehicle drive can provide and the drive torque required for driving the vehicle. In this manner, during an acceleration or starting maneuver required by the driver, the cooling power of the air conditioner is reduced only to the level required for actually performing the acceleration or starting maneuver with the desired acceleration. For this purpose, the compressor generally does not have to be shut off completely, but continues operating at the reduced power subject to the respective limit. As a result, optimum cooling of the vehicle interior and improved air conditioning comfort is achieved and unnecessary switching processes involving the compressor that compresses the coolant are avoided.